The present invention relates to a combustion chamber construction for an internal combustion engine with a direct fuel injection system, and more particularly to an arrangement of elements in a combustion chamber of the engine for promoting stratified combustion.
It is preferable that, in a light engine load range, an air-fuel mixture becomes rich near a spark plug at a later stage of the compression stroke, because the combustion is stably performed even if the air-fuel mixture is extremely lean in the entire zone. Thus, fuel consumption is improved.
In order to improve the stratified combustion in the light engine load range, a direct fuel injection system has been proposed. The engine having such an injection system is called a direct injection stratified charge (DISC) engine. In the system, the fuel is directly injected into a combustion chamber of the cylinder by a fuel injector provided in the cylinder.
In the combustion chamber, an intake valve and an exhaust valve are also disposed. Therefore, the design for the arrangement of the fuel injector is limited by disposition of the intake and exhaust valves. In particular, in an engine having two intake valves and two exhaust valves in each cylinder, the design for disposing the fuel injector is further limited because two intake ports and two exhaust ports are formed in a cylinder head.
Japanese Patent Application Laid-open No. 62-82222 discloses a DISC engine having four valves in which spark plug is provided between the exhaust ports in an inclined position and a fuel injector is provided between the intake ports in an inclined position. In Japanese Patent Application Laid-open No. 63-189614, a spark plug is provided on a central position of a combustion chamber in a vertical position and a fuel injector is provided between the intake ports in an inclined position
In the conventional engines, a nozzle of the fuel injector is disposed far away from an electrode of the spark plug. Therefore, it is difficult to accurately control an air-fuel mixture near the spark plug. As a result, ignitability of the fuel reduces, causing unstable combustion of the fuel.
Furthermore, since the fuel injector is provided in the inclined position, spray of fuel is directed to the wall of the cylinder and the fuel is cooled by the wall of the cylinder, whereby the combusion operation deteriorates.
If quantity of injected fuel is increased at an advanced fuel injection timing, a part of the fuel spray directly impacts the wall of the cylinder, which causes an increase of HC emission and a reduction of lubrication effect on the cylinder liner.